Here are the methods I use to find the MasterCodes for NDS Games:
And some common question people might ask.

Method 1:
Use ndsmas.....Usage, in DOS command promt, type ndsmas name.nds
Well, ndsmas detected a MasterCode, but the codes don't work or you got 2 blank screens when the game loads, what's wrong?
Chances are:
1. if all the codes don't work, then the MasterCode that ndsmas detected might not be the correct one, like in the case of Advance War DS.
2. if you only got 2 blank screens, then you might need to add a line infron of the Mastercode that starts with Cxxxxxxx xxxxxxxx.

Method 2:
Use ndsdis.....Usage, in DOS command prompt, type ndsdis name.nds > name.txt
1. Open name.txt with wordpad and SEARCH for 0x04000130 and when you get a result
2. SEARCH for E12FFF1E